1. Field of the Invention
The present invention relates to a wire saw apparatus for sawing or cutting an article to be processed, hereinafter referred to a work simply, e.g., a brittle material such as a semiconductor material, a magnetic material, quartz, ceramic or the like, into a plurality of slices.
2. Description of Related Art
In recent years, in order to manufacture a large number of wafer-like pieces by cutting a work having a large diameter, a wire saw apparatus has been used. An example thereof is illustrated in FIG. 5. In this Figure, the wire saw apparatus 1 comprises a wire supply spool 3 for supplying a cutting wire 2, a cutting head 5 for cutting a work 4 by using the cutting wire 2, and a wire take-up spool 6 for taking-up the cutting wire 2. In the wire saw apparatus 1, a plurality of guide rollers 7, 7, . . . for guiding the cutting wire 2 and for giving a predetermined tension to the cutting wire 2 are arranged between the wire supply spool 3 and the cutting head 5 and between the cutting head 5 and the wire take-up spool 6. The cutting head 5 comprises three main rollers 5a, 5b, and 5c. In the wire saw apparatus 1, the work 4 is sawed or cut by pushing the work 4 against a plurality of lines of cutting wire 2 which is wrapped around the main rollers 5a, 5b, and 5c of the cutting head 5 in a spiral configuration, and by supplying an abrasive slurry containing abrasive grains into between the work 4 and the lines of cutting wire 2, while complex action of the cutting wire 2 which comprises back and forth action in the direction of the lines and feeding action, is taken.
In such a conventional wire saw apparatus, the wrapping angle of portions of the cutting wire 2, which is wrapped around a guide roller 7 and are in contact with the guide rollers 7, is only about 180.degree. at the most. Because of such a small wrapping angle of the cutting wire 2, the wire 2 is apt to become loose while cutting the work 4. As a result, a stress concentration is apt to occur in a portion of the wire 2, so that a breakage of the wire 2 occurs. When such a breakage of the wire occurs, work for stretching the cutting wire 2 again is required. There is a problem that such work for re-stretching of the wire is laborious and requires a long time.
Each guide roller 7 has a groove 9 having a V-shaped section, which may be hereinafter simply referred to a V-shaped groove, on the peripheral surface thereof, as shown in FIG. 6. Therefore, the cutting wire 2 in the groove 9 is seated on the bottom of the groove 9 when some tension is applied to the wire 2. However, when the cutting wire 2 comes loose, the wire 2 rolls and moves in the V-shaped groove 9, so that partial wear is produced on the wall surface of the groove. When such partial wear is produced, replacement of the guide roller 7 is required. Because the replacement work includes work for stretching the cutting wire 2 again and the like, there is a problem that the work is laborious and requires a long time. Some known wire saw apparatuses adopt guide rollers 7a or 7b each of which has one or more spare peripheral grooves 9a with a V-shaped section, as shown in FIGS. 7 and 8. Such a type of wire saw apparatus having such guide rollers 7a or 7b with spare peripheral grooves 9a , has the disadvantages of requiring higher manufacturing costs and of being large-sized.